WARNING: Emergency contraception - also known as the "morning-after pill"
Usually a progestin-only product, i.e. it is an estrogen-free drug.
Used in case of unprotected sexual intercourse, contraceptive failure, missed birth control pill, or broken condom.
It does not protect against sexually-transmitted infections, including AIDS.
Emergency contraception should only be used in exceptional cases, not in place of regular contraception.
Do NOT use as a contraceptive - ONLY in an emergency - it is supposed to be a once off. Even infrequent use can have a disastorous effect on your body, which includes malfuntion of your hormonal system and infertility.
http://en.wikipedia.org/wiki/Emergency_contraception